SAN FRANCISCO—Catalyst Biosciences Inc., a clinical-
stage biopharmaceutical company focused on developing novel medicines to address hematology indications, has announced positive preclinical results in well-
validated models of hemophilia A and B with marzeptacog alfa (activated), a next-generation coagulation factor VIIa, and CB 2679d/ISU304, a next-generation
coagulation factor IX.

The results highlight the attractive pharmacodynamics and pharmacokinetic profiles of both
coagulation factors based on bioavailability, potency, time to maximal concentration and half-life that should allow for subcutaneous (SQ) dosing in
individuals with hemophilia.

Dr. Howard Levy, chief medical officer at Catalyst Biosciences tells DDNews,
“Marzeptacog alfa (activated) is a next-generation increased potency factor VIIa that was designed to allow for effective, long-term,
subcutaneous prophylaxis in hemophilia patients with inhibitors. Marzeptacog alfa was designed to combine higher clot-generating activity at the site of
bleeding and therefore improved efficacy. Half-life is extended when dosed subcutaneously.”

Catalyst plans
to initiate a SQ efficacy trial of marzeptacog alfa in individuals with hemophilia B in 2017. Levy says Catalyst aims to initially study marzeptacog alfa in
hemophilia B, because a major competitor’s drug cannot be used in hemophilia B.

In addition, Catalyst and
its collaboration partner, ISU Abxis, plan to initiate a Phase 1/2 proof-of-concept IV/SQ clinical trial of CB 2679d/ISU304 in individuals with hemophilia B
in the second quarter of 2017. Levy states, “Catalyst has a collaboration with ISU Abxis to advance the development of CB 2679d/ISU304 through Phase
1/2 proof-of-concept study in individuals with hemophilia B.”

According to Levy, Catalyst entered into a
co-development agreement with ISU Abxis in 2013. “ISU Abxis is responsible for preclinical development activities and clinical development through a
proof-of-concept Phase 1 study in hemophilia B patients. After Phase 1, ISU Abxis retains an option for exclusive commercial rights in Korea, while Catalyst
retains full development and commercial rights for CB 2679d/ISU304 outside of Korea,” Levy notes.

When asked
what made CB 2679d/ISU304 different from other drugs currently on the market, Levy told DDNews, “CB 2679d/ISU304 has shown significantly
higher potency in preclinical studies versus other factor IX products on the market and in development. All currently available factor IX products are
administered intravenously, while CB 2679d/ISU304 is intended for subcutaneous dosing. Catalyst believes that CB 2679d/ISU304 may provide hemophilia B
patients with a viable subcutaneous prophylactic therapy.”

“These results demonstrate that CB
2679d/ISU304 has significantly higher potency compared with other factor IX products and has the potential to be dosed by SQ injection and achieve stable
normal activity levels—an attribute shared by no other factor IX product on the market or in clinical development,” said Dr. Nassim Usman,
president and CEO of Catalyst. “In addition, in the marzeptacog alfa (activated) SQ preclinical results, daily SQ dosing achieved steady-state levels
of factor VIIa sufficient to correct coagulation abnormalities.”

The results of the studies on the two
compounds were presented in poster sessions at the European Association of Hemophilia and Allied Disorders 10th Annual Congress in Paris.